Peptide, Enzyme, Protein: What’s The Difference And Does It Matter?

Proteins

The best way to do this is take them in reverse. Away from sites like ours, the most widespread use of the word protein refers to the main component of our diet that is not fat, carbohydrate, or water. As a scientific term, however, proteins are molecules that contain at least one long chain of amino acids. The astonishing diversity and capacities of life are in large part down to the fact that amino acids can be arranged in so many ways, making up such a variety of proteins that organisms can put to such innovative uses.

Each human cell has been calculated to contain an average of 1-3 billion protein molecules, giving some sense of their importance and abundance. Genes provide the code to create specific proteins, but there are only (if that’s the word) about 20,000 proteins coded for by the human genome, not all of which will be in a specific cell. A cell, therefore, will contain thousands or millions of copies of a specific protein.

Proteins are also structural, providing the strength and resilience for cells, tissues, hair, and much else.

Enzymes

Enzymes are large molecules that make things happen within the body without being changed themselves; that is, they’re catalysts that speed up the rate of chemical reactions. They’re discussed here because most enzymes are proteins.

Chemical reactions often take place at frustratingly slow rates. A lifeform that can speed reactions up has a major evolutionary advantage, so it’s not surprising that billions of years of evolution have led to enzymes driving thousands of reactions, including most of those our body routinely undertakes.

For a long time, it was thought that all large molecule catalysts were proteins, so it was straightforward to define enzymes as the subgroup of proteins that speed up biological reactions.

However, ribozymes (ribonucleic acid enzymes) are RNA molecules with a similar capacity to accelerate chemical reactions necessary for life. Their discovery in 1982 forced a recognition that while enzymes overlap with proteins, they’re not a perfect subset. 

Complicating things further, one of the most common and important biocatalysts is the ribosome, used to make proteins by linking amino acids together according to instructions carried by messenger RNA. A ribosome is composed of a combination of RNA and proteins, needing both to do its job.

Peptides

Peptides are short chains of amino acids linked by a chemical connection known as a peptide bond. Proteins fold to prevent becoming ridiculously long, but peptides are linear or have only simple folds.

Peptides often combine to form what are known as polypeptides, provided the chains don’t branch. A polypeptide with a molecular mass of more than 10,000 Daltons (a unit equal to one twelfth the mass of a carbon atom) is generally classified as a protein, although people can get a bit flexible on this definition. More or fewer than 50 amino acids is also used to distinguish the two, although US regulators use 40 amino acids as the line for some reason. Molecules with multiple polypeptides joined together so that they branch are also considered proteins.

Besides their smaller size and relatively simple shape, peptides tend to perform different roles from proteins. They act as signal carriers within the body, and affect the operation of larger molecules. On the other hand, as noted above, proteins perform a dazzling array of functions in living organisms. 

Although organisms have been making peptides for billions of years, peptides’ relative simplicity means they can often be synthesized chemically, whereas proteins usually need to be made by cells. 

Although the peptide-protein dividing line may be a bit flexible, it can also be an important one when it comes to medication safety. A peptide can reach more places in the body than a protein, and is usually more easily absorbed. By virtue of their greater complexity, medications containing proteins are treated as needing more oversight, but peptides become degraded more easily.